This invention relates in general to compositions to remove ice, snow and/or frost (“frozen precipitation”) from surfaces and/or to prevent ice from forming on surfaces, and in particular to deicing/anti-icing fluids.
De-icing/anti-icing fluids are used on many different surfaces where frozen precipitation is a problem. Deicing involves the application of a deicing fluid onto frozen precipitation that has already formed in order to remove it from a surface. The deicing fluid melts the frozen precipitation by lowering its freezing point. Anti-icing involves the application of an anti-icing fluid onto a surface before ice is present, thereby lowering the freezing point of any precipitation that contacts the surface and preventing it from turning into ice. Some fluids are useful for both de-icing and anti-icing, while others are particularly useful for one or the other.
In a particular application, deicing/anti-icing fluids are used in the airline industry. Aircraft deicing fluids (ADF) are formulated to remove ice, snow and frost from the exterior surfaces of aircraft. They are also formulated to flow easily from the aircraft surfaces during takeoff and to minimize effects on aerodynamic performance at low temperatures. Runway deicing fluids (RDF) are formulated to deice and anti-ice airport runways and taxiways. They penetrate and break the bond between packed snow and ice and the runway/taxiway surface, thus facilitating the removal of the frozen accumulation by mechanical means. They also decrease the potential for ice formation on the runway/taxiway.
Aircraft deicing fluids are usually composed of water, a freezing point depressant, and an additive package. The freezing point depressant is typically ethylene glycol, diethylene glycol, or propylene glycol. The glycol-based fluids are effective deicers, but they are often considered to be harmful to the environment, particularly if applied in large volumes. Consequently, there is a need for environmentally friendly deicing/anti-icing fluids that perform comparably to the glycol-based fluids.
The additive packages of aircraft deicing fluids usually include wetting agents, pH buffers, antioxidants, antiprecipitation agents, dyes, foam suppressors, and in many cases corrosion control and fire inhibitors. The wetting agents of choice of aircraft deicing fluids are nonylphenol ethoxylates such as octylphenol ethoxylates and alcohol ethoxylates. The nonylphenol ethoxylates are low-cost, nonionic wetting agents that reduce surface tension and are characterized by low foaming potential. However, one of their breakdown products, nonylphenol, is a known endocrine disruptor and could present a danger to the receiving water from an airport engaged in aircraft deicing operations. (Corsi, Steven R., et al. “Nonylphenol Ethoxylates and Other Additives in Aircraft Deicers, Antiicers, and Waters Receiving Airport Runoff,” Environmental Science and Technology, Vol. 37, No. 18, 2003, pp. 4031–4037.) Therefore, it would be advantageous to provide improved wetting agents for deicing/anti-icing fluids.
Several patents disclose aircraft deicing/anti-icing fluids containing sorbitol and/or glycerol as a freezing point depressant instead of a glycol. For example, U.S. Pat. No. 6,129,857 to Sapienza discloses aircraft deicing/anti-icing fluids containing sorbitol, water and other ingredients. U.S. Pat. No. 5,993,684 to Back et al. discloses aircraft deicing fluids containing glycerol, sorbitol and water, and optionally materials such as thickeners, antioxidants, pH adjusters, stabilizers, biocides, or corrosion inhibitors. International Patent Publication No. WO 01/29146 A1 to Westmark et al. discloses aircraft deicing fluids containing glycerol, nonionic surfactant, polysaccharide thickener, and water. There is still a need for improved deicing/anti-icing fluids.